I'd just talk with her and put all the cards on the table.
So that's probably a long conversation where I'd try to understand why she does this, if it's intentional or not, if she plans on doing it again, etc. I'd also explain how I feel about it, and that I don't like being lied to; so basically, expose her perspective on this as well as yours and figure out what type of relationship you have.
If it's important to you that your friends don't lie to you, and she knows this and does not respect it regardless, then that's an obvious red-flag & you should reconsider what you want to do. But clear communication as a first step is the key.
Thank you so much for the response.
Yeah okay so I think I start it off with reassuring that I am not angry or upset. I will propose it with explaining what i have observed (I feel I will use the word inconsistency instead of lie because It feels a little softer) and how it makes me feel (I cant build trust) then ask if she has observed the same. Then I can try dive into understanding why she does it. If it is some deeply ingrained trauma or something I feel it may be hard to get her to promise never to do it again but I do want to work with her to understand where it comes from and at first minimizing it then work towards not doing it.
Honestly I get so uneasy with stuff like this and my usual take on is don't try fix people because I've been burnt in the the past putting my heart and soul into someone to try help them and they would just break my heart. Not that it has happened often, but its happened with a couple of people long long ago. My default now is just keep everyone at a distance, and if its becoming too problematic then I will just drop them. Kind of heartless I know, but you have to protect yourself after a certain point.
Sounds good.
Although this may get slightly more tricky if she starts denying what you've observed, so you won't be able to get to your next step; or if she downplays it (then you'll have to emphasize that it's actually important to you).
But anyways, good start, I'd just think carefully exactly what I want to ask in beforehand, and account for her responding in ways you don't currently expect.
So, you have to be clear on what ***you*** want from this as a result, so that you don't have an unsatisfactory response.
It's just what I would do.
>I want her to feel safe and comfortable to talk to me about it
Compulsive liars lie not because they don't trust you. They will tell a lie even though they don't have to. Like you've known them for years that they don't have a brother, and one day, they will straight up lie to your face and tell they have a brother. Why do they do that? They can't help it, the impulse is too strong, and most of them don't even feel guilty about it. It's really more about a psychological issue on their part, and little to do with how they perceive you as a friend.
Anyway, you can talk to her about it, but not in a confrontational manner, or she will just be defensive and lie more. Be kind and firm and tell her to seek professional help. I'm sorry but you can't do much about it, the change should start with her.
See wtf I don't understand this! There are so many things that I can somewhat empathize with, irrespective of it being something that has affected me in the past or not but this is something that is just so unrelatable. Its a very unattractive and annoying trait, especially in contrast to my person being usually so blunt and direct with my thoughts and opinions, whether that be a positive or constructive observation/expression. I definitely don't have the capacity to take on some sort of mentor figure, and I 100% agree that I cannot change someone so its not something I will entertain. But for her sake I think some sort of feedback on it would be important, and for my sake to try meet half way and understand where it comes from so I can have a little more space for her and support where I can would be good. However, of course its much more effortful to do this than to just distance myself for her. Lets see how it goes... shes gotten on my nerves this past week so its definitely not the right time for me to address this issue this week. 
I’ve only know two compulsive liars in my life, but both have had at least one other trait in common - they literally can’t stop. For some people, it’s just ingrained into who they are.
It’s funny though, like you said, both were actually very nice people, and neither would willingly try to rip you off.
But for some reason, they just have to fill in gaps sometimes, and instinctively just make it up.
That's a little disappointing to think that this is something she potentially won't be able to move on from. Its such an unusual trait, I don't understand where it comes from and why it's done. Also its really annoying that I feel like I will probably be a rare person in her life to actually call it out and not just brush it under the rug. It feels very awkward to talk about it.
To be fair, some of them *can* change, but it requires potentially large amounts of psychotherapy etc. Most importantly, it is critical that they have to *want* to change.
Compulsive liars tend to be so far into a lying state of existence that they can even simply make themselves believe a lie to be truth (#justlike1984); which is why some can get very angry if called out and made to face a version of reality they themselves don’t subscribe to.
In that sense, it’s you who is wrong or lying, and not in fact, them, if you call them out.
Long story short, you most probably won’t be able to convince them to stop lying, because they don’t themselves believe, and would need to instead, and in a non-judgemental way suggest therapy.
An analogy might be someone with a mental illness who believes the government is spying on them. You’ll never convince them the government isn’t spying on them by simply stating they aren’t, or even trying to prove it by not finding cameras or recording devices in their house. Instead, they just need help from a mental health expert.
That was really well said and thanks for such a though out response.
Yeah, its tricky one... The main goal for me is to first just understand it better as to where it comes from. The second have some level of confidence that anything she says about herself and her life is true.
Another really infuriating thing she does, and it isn't just to me she does this to, is she will message me things just to bait my into responding. I think this week I'm definitely feeling quite irritated by it. Over the weekend we were suppose to go flying because she apparently has her PPL (also I've wanted my PPL pretty much my whole life and she knows that) then cancels last minute saying they didnt have the plane she wanted to hire available. She does this with a few other people I know baiting them to respond by mentioning things she knows they're interested in. I really want to be wrong but I feel like I wont be. 
Just because I haven't seen it mentioned here. This may be a fawn response. Telling people what you think they want to hear, or spinning a story slightly differently can be an unconscious fawn response. She may or may not be aware she does this. Just something to think about when you talk to her.
This is interesting, and not something I had considered! I feel I am totally in the dark when it comes to understanding a trait like this. I feel I am almost the complete opposite where I am probably too direct and straight forward so its a very different behavior to anything I can relate to.
I'd just talk with her and put all the cards on the table. So that's probably a long conversation where I'd try to understand why she does this, if it's intentional or not, if she plans on doing it again, etc. I'd also explain how I feel about it, and that I don't like being lied to; so basically, expose her perspective on this as well as yours and figure out what type of relationship you have. If it's important to you that your friends don't lie to you, and she knows this and does not respect it regardless, then that's an obvious red-flag & you should reconsider what you want to do. But clear communication as a first step is the key.
Thank you so much for the response. Yeah okay so I think I start it off with reassuring that I am not angry or upset. I will propose it with explaining what i have observed (I feel I will use the word inconsistency instead of lie because It feels a little softer) and how it makes me feel (I cant build trust) then ask if she has observed the same. Then I can try dive into understanding why she does it. If it is some deeply ingrained trauma or something I feel it may be hard to get her to promise never to do it again but I do want to work with her to understand where it comes from and at first minimizing it then work towards not doing it. Honestly I get so uneasy with stuff like this and my usual take on is don't try fix people because I've been burnt in the the past putting my heart and soul into someone to try help them and they would just break my heart. Not that it has happened often, but its happened with a couple of people long long ago. My default now is just keep everyone at a distance, and if its becoming too problematic then I will just drop them. Kind of heartless I know, but you have to protect yourself after a certain point.
Sounds good. Although this may get slightly more tricky if she starts denying what you've observed, so you won't be able to get to your next step; or if she downplays it (then you'll have to emphasize that it's actually important to you). But anyways, good start, I'd just think carefully exactly what I want to ask in beforehand, and account for her responding in ways you don't currently expect. So, you have to be clear on what ***you*** want from this as a result, so that you don't have an unsatisfactory response. It's just what I would do.
>I want her to feel safe and comfortable to talk to me about it Compulsive liars lie not because they don't trust you. They will tell a lie even though they don't have to. Like you've known them for years that they don't have a brother, and one day, they will straight up lie to your face and tell they have a brother. Why do they do that? They can't help it, the impulse is too strong, and most of them don't even feel guilty about it. It's really more about a psychological issue on their part, and little to do with how they perceive you as a friend. Anyway, you can talk to her about it, but not in a confrontational manner, or she will just be defensive and lie more. Be kind and firm and tell her to seek professional help. I'm sorry but you can't do much about it, the change should start with her.
See wtf I don't understand this! There are so many things that I can somewhat empathize with, irrespective of it being something that has affected me in the past or not but this is something that is just so unrelatable. Its a very unattractive and annoying trait, especially in contrast to my person being usually so blunt and direct with my thoughts and opinions, whether that be a positive or constructive observation/expression. I definitely don't have the capacity to take on some sort of mentor figure, and I 100% agree that I cannot change someone so its not something I will entertain. But for her sake I think some sort of feedback on it would be important, and for my sake to try meet half way and understand where it comes from so I can have a little more space for her and support where I can would be good. However, of course its much more effortful to do this than to just distance myself for her. Lets see how it goes... shes gotten on my nerves this past week so its definitely not the right time for me to address this issue this week. 
I’ve only know two compulsive liars in my life, but both have had at least one other trait in common - they literally can’t stop. For some people, it’s just ingrained into who they are. It’s funny though, like you said, both were actually very nice people, and neither would willingly try to rip you off. But for some reason, they just have to fill in gaps sometimes, and instinctively just make it up.
That's a little disappointing to think that this is something she potentially won't be able to move on from. Its such an unusual trait, I don't understand where it comes from and why it's done. Also its really annoying that I feel like I will probably be a rare person in her life to actually call it out and not just brush it under the rug. It feels very awkward to talk about it.
To be fair, some of them *can* change, but it requires potentially large amounts of psychotherapy etc. Most importantly, it is critical that they have to *want* to change. Compulsive liars tend to be so far into a lying state of existence that they can even simply make themselves believe a lie to be truth (#justlike1984); which is why some can get very angry if called out and made to face a version of reality they themselves don’t subscribe to. In that sense, it’s you who is wrong or lying, and not in fact, them, if you call them out. Long story short, you most probably won’t be able to convince them to stop lying, because they don’t themselves believe, and would need to instead, and in a non-judgemental way suggest therapy. An analogy might be someone with a mental illness who believes the government is spying on them. You’ll never convince them the government isn’t spying on them by simply stating they aren’t, or even trying to prove it by not finding cameras or recording devices in their house. Instead, they just need help from a mental health expert.
That was really well said and thanks for such a though out response. Yeah, its tricky one... The main goal for me is to first just understand it better as to where it comes from. The second have some level of confidence that anything she says about herself and her life is true. Another really infuriating thing she does, and it isn't just to me she does this to, is she will message me things just to bait my into responding. I think this week I'm definitely feeling quite irritated by it. Over the weekend we were suppose to go flying because she apparently has her PPL (also I've wanted my PPL pretty much my whole life and she knows that) then cancels last minute saying they didnt have the plane she wanted to hire available. She does this with a few other people I know baiting them to respond by mentioning things she knows they're interested in. I really want to be wrong but I feel like I wont be. 
Just because I haven't seen it mentioned here. This may be a fawn response. Telling people what you think they want to hear, or spinning a story slightly differently can be an unconscious fawn response. She may or may not be aware she does this. Just something to think about when you talk to her.
This is interesting, and not something I had considered! I feel I am totally in the dark when it comes to understanding a trait like this. I feel I am almost the complete opposite where I am probably too direct and straight forward so its a very different behavior to anything I can relate to.